EPA

United States Office of Water 

Environmental Protection Washington DC September 2002 

Agency 20460 

EPA 821-R-02-023 

Method 1603: Escherichia coli 

(E. coli) in Water by Membrane

Filtration Using Modified

membrane-Thermotolerant 

Escherichia coli Agar

(Modified mTEC) 
U.S. Environmental Protection Agency 

Office of Water (4303T) 

1200 Pennsylvania Avenue, NW 

Washington, DC 20460 

EPA-821-R-02-023
Disclaimer 

The Engineering and Analysis Division, of the Office of Science and Technology, has reviewed and 

approved this report for publication. The Office of Science and Technology directed, managed, and 

reviewed the work of DynCorp in preparing this report. Neither the United States Government nor any of 

its employees, contractors, or their employees make any warranty, expressed or implied, or assumes any 

legal liability or responsibility for any third party’s use of or the results of such use of any information, 

apparatus, product, or process discussed in this report, or represents that its use by such party would not 

infringe on privately owned rights. This document combines the information previously published in Test 

Methods for Escherichia coli and Enterococci in Water by the Membrane Filter Procedure (EPA-600/4-

85-076) (Reference 18.6 and Improved Enumeration Methods for the Recreational Water Quality 

Indicators: Enterococci and Escherichia coli (EPA/821/R-97/004) (Reference 18.4. Mention of trade 

names or commercial products does not constitute endorsement or recommendation for use. 

Questions concerning this method or its application should be addressed to: 

Robin K. Oshiro

Engineering and Analysis Division (4303T)

U.S. EPA Office of Water, Office of Science and Technology

1200 Pennsylvania Avenue, NW

Washington, DC 20460

oshiro.robin@epa.gov

202-566-1075

202-566-1053 (facsimile)
Table of Contents 

1.0 Scope and Application ......................................................... 1

2.0 Summary of Method ........................................................... 1

3.0 Definitions ................................................................... 1

4.0 Interferences and Contamination ................................................. 1

5.0 Safety ...................................................................... 1

6.0 Equipment and Supplies ........................................................ 2

7.0 Reagents and Standards ........................................................ 3

8.0 Sample Collection, Preservation, and Storage ....................................... 6

9.0 Quality Control ............................................................... 6

10.0 Calibration and Standardization .................................................. 6

11.0 Procedure ................................................................... 6

12.0 Data Analysis and Calculations .................................................. 7

13.0 Method Performance ........................................................... 7

14.0 Reporting Results ............................................................. 8

15.0 Verification Procedure ......................................................... 8


16.0 Pollution Prevention ........................................................... 9


17.0 Waste Management ............................................................ 9

18.0 References ................................................................... 9
Method 1603: Escherichia coli (E. coli) in Water by Membrane 

Filtration Using Modified membrane- Thermotolerant Escherichia coli 

Agar (modified mTEC) 

September 2002 

1.0 Scope and Application 

1.1 This method describes a revised Escherichia coli membrane filter (MF) procedure, a single-step 

method that uses one medium, modified mTEC Agar, and does not require the transfer of the 

membrane filter to another medium or other substrate. The modified medium contains a 

chromogen (5-bromo-6-chloro-3-indolyl-$-D-glucuronide), which is catabolized to glucuronic 

acid and a red- or magenta-colored compound by E. coli that produce the enzyme $-Dglucuronidase. The apparatus and equipment, and sampling, filtration, and verification procedures 

for this modified mTEC method are identical to those of the original mTEC method. Because the 

bacterium is a natural inhabitant only of the intestinal tract of warm-blooded animals, its presence 

in water samples is an indication of fecal pollution and the possible presence of enteric pathogens. 

1.2 The E. coli test is used as a measure of recreational water quality. Epidemiological studies have 

led to the development of criteria which can be used to promulgate recreational water standards 

based on established relationships between health effects and water quality. The significance of 

finding E. coli in recreational water samples is the direct relationship between the density of E. 

coli and the risk of gastrointestinal illness associated with swimming in the water (Reference 

18.3. 

1.3 The test for E. coli can be applied to fresh, estuarine, and marine waters. 

1.4 Since a wide range of sample volumes or dilutions can be analyzed by the MF technique, a wide 

range of E. coli levels in water can be detected and enumerated. 

2.0 Summary of Method 

2.1 The MF method provides a direct count of E. coli in water based on the development of colonies 

that grow on the surface of a membrane filter. A water sample is filtered through the membrane, 

which retains the bacteria. After filtration, the membrane containing the bacteria is placed on a 

selective and differential medium, modified mTEC Agar, incubated at 35 ± 0.5°C for 2 h to 

resuscitate the injured or stressed bacteria, and then incubated at 44.5 ± 0.2°C for 22 h. The 

modified method eliminates the transfer of the membrane filter to another substrate. The target 

colonies on modified mTEC agar are red or magenta in color after the incubation period. 

3.0 Definitions 

3.1 In this method, E. coli are those bacteria which produce red or magenta colonies on the modified 

mTEC agar. 

4.0 Interferences and Contamination 

4.1 Water samples containing colloidal or suspended particulate material can clog the membrane 

filter and prevent filtration, or cause spreading of bacterial colonies which could interfere with 

identification of target colonies. 

5.0 Safety 

September 2002 
Method 1603 

5.1 The analyst/technician must know and observe the normal safety procedures required in a

microbiology laboratory while preparing, using, and disposing of cultures, reagents, and materials

and while operating sterilization equipment.

5.2 Mouth-pipetting is prohibited.

6.0 Equipment and Supplies

6.1 Glass lens with magnification of 2-5x, or stereoscopic microscope.

6.2 Lamp, with a cool, white fluorescent tube.

6.3 Hand tally or electronic counting device.

6.4 Pipet container, stainless steel, aluminum or borosilicate glass, for glass pipets.

6.5 Pipets, sterile, T.D. bacteriological or Mohr, glass or plastic, of appropriate volume.

6.6 Graduated cylinders, 100-1000 mL, covered with aluminum foil or kraft paper and sterile.

6.7 Membrane filtration units (filter base and funnel), glass, plastic or stainless steel, wrapped with

aluminum foil or kraft paper and sterilized.

6.8 Ultraviolet unit for sanitization of the filter funnel between filtrations (optional).

6.9 Line vacuum, electric vacuum pump, or aspirator for use as a vacuum source. In an emergency or

in the field, a hand pump or a syringe equipped with a check valve to prevent the return flow of

air, can be used.

6.10 Filter flask, vacuum, usually 1 L, with appropriate tubing. A filter manifold to hold a number of

filter bases is optional.

6.11 Flask for safety trap placed between the filter flask and the vacuum source.

6.12 Forceps, straight or curved, with smooth tips to handle filters without damage.

6.13 Ethanol, methanol or isopropanol in a small, wide-mouth container, for flame-sterilizing forceps.

6.14 Burner, Bunsen or Fisher type, or electric incinerator unit for sterilizing loops and needles.

6.15 Thermometer, checked against a National Institute of Standards and Technology (NIST) certified

thermometer, or one that meets the requirements of NIST Monograph SP 250-23.

6.16 Petri dishes, sterile, plastic, 9 x 50 mm, with tight-fitting lids; or 15 x 60 mm, glass or plastic,

with loose-fitting lids; or 15 x 100 mm.

6.17 Bottles, milk dilution, borosilicate glass, screw-cap with neoprene liners, marked at 99 mL for

1:100 dilutions. Dilution bottles marked at 90 mL or tubes marked at 9 mL may be used for 1:10

dilutions.

6.18 Flasks, borosilicate glass, screw-cap, 250-2000 mL volume.

6.19 Membrane filters, sterile, white, grid marked, 47 mm diameter, with 0.45 ± 0.02 μm pore size.

September 2002 2 
Method 1603 

6.20 Inoculation loops, at least 3 mm diameter, and needles, nichrome or platinum wire, 26 B & S 

gauge, in suitable holders. Sterile disposable applicator sticks or plastic loops are alternatives to 

inoculation loops. 

Note: A platinum loop is required for the cytochrome oxidase test in the verification procedure. 

6.21 Incubator maintained at 35 ± 0.5°C, with approximately 90% humidity if loose-lidded petri dishes 

are used. 

6.22 Waterbath maintained at 44.5 ± 0.5°C. 

6.23 Waterbath maintained at 50°C for tempering agar. 

6.24 Test tubes, 20 x 150 mm, borosilicate glass or plastic. 

6.25 Test tubes, 10 x 75 mm, borosilicate glass 

6.26 Caps, aluminum or autoclavable plastic, for 20 mm diameter test tubes. 

6.27 Test tubes screw-cap, borosilicate glass, 16 x 125 mm or other appropriate size. 

6.28 Filter Paper. 

6.29 Whirl-Pak® bags. 

7.0 Reagents and Standards 

7.1 Purity of Reagents: Reagent grade chemicals shall be used in all tests. Unless otherwise 

indicated, reagents shall conform to the specifications of the Committee on Analytical Reagents 

of the American Chemical Society (Reference 18.5). The agar used in preparation of culture 

media must be of microbiological grade. 

7.2 Whenever possible, use commercial culture media as a means of quality control. 

7.3 Purity of Water: Reagent water conforming to Specification D1193, reagent water conforming 

Type II, Annual Book of ASTM Standards (Reference 18.1). 

7.4 Phosphate Buffered Saline 

7.4.1 Composition: 

Sodium Dihydrogen Phosphate 0.58 g 

Sodium Monohydrogen Phosphate 2.5 g 

Sodium Chloride 8.5 g 

Reagent-Grade Distilled Water 1.0 L 

7.4.2 Preparation: Dissolve the ingredients in 1 L of reagent-grade distilled water in a flask , 

and dispense in appropriate amounts for dilutions in screw-cap bottles or culture tubes, 

and/or into containers for use as rinse water. Autoclave at 121°C (15 lb pressure) for 15 

min. Final pH should be 7.4 + 0.2. 

7.5 Phosphate Buffered Dilution Water (References 18.2) 

3 September 2002 
Method 1603 

7.5.1 Composition of Stock Phosphate Buffer Solution: 

Phosphate Dihydrogen Phosphate 34.0 g 

Reagent-Grade Distilled Water 500.0 mL 

Preparation: Adjust the pH of the solution to 7.2 with 1 N NaOH, and bring the volume to 

1 L with reagent-grade distilled water. Sterilize by filtration or autoclave at 121°C (15 lb 

pressure) for 15 min. 

7.5.2 Preparation of Stock Magnesium Chloride Solution: Add 38 g anhydrous MgCl2 or 81.1 

g MgCl2C6H2O to 1 L reagent-grade distilled water. Sterilize by filtration or autoclave at 

121°C (15 lb pressure) for 15 min. 

7.5.3 Storage of Stock Solutions: After sterilization, store the stock solutions in the refrigerator 

until used. Handle aseptically. If evidence of mold or other contamination appears, the 

affected stock solution should be discarded and a fresh solution should be prepared. 

7.5.4 Working Phosphate Buffered Dilution Water: Mix 1.25 mL of the stock phosphate buffer 

and 5 mL of the MgCl2 stock per liter of reagent-grade distilled water. Dispense in 

appropriate amounts for dilutions in screwcap bottles or culture tubes, and/or into 

containers for use as rinse water. Autoclave at 121°C (15 lb pressure) for 15 min. Final 

pH should be 7.0 ± 0.2. 

7.6 Modified mTEC Agar (Difco 214884 or 214880) 

7.6.1 Composition: 

Protease Peptone #3

Yeast Extract

Lactose

NaCl

Dipotassium Phosphate

Monopotassium Phosphate

Sodium Lauryl Sulfate 

Sodium Desoxycholate

Chromogen 

(5-bromo-6-chloro-3-indolyl-

$-D-glucuronide) 

Agar 

Reagent-Grade Distilled Water 

5.0 g 

3.0 g 

10.0 g 

7.5 g 

3.3 g 

1.0 g 

0.2 g 

0.1 g 

0.5 g 

15.0 g 

1.0 L 

7.6.2 Preparation: Add 45.6 g dehydrated modified mTEC Agar to 1 L of reagent-grade 

distilled water in a flask, and heat to boiling until the ingredients dissolve. Autoclave at 

121°C (15 lb pressure) for 15 min, and cool in a 50°C waterbath. Pour the medium into 

each 9 x 50 mm culture dish to a 4-5 mm depth (approximately 4-6 mL), and allow to 

solidify. Final pH should be 7.3 ± 0.2. Store in a refrigerator. 

7.7 Nutrient Agar (Difco 0001, BD 4311472) 

7.7.1 Composition: 

Peptone 5.0 g 

Beef Extract 3.0 g 

Agar 15.0 g 

Reagent-Grade Distilled Water 1.0 L 

September 2002 4 
Method 1603 

7.7.2 Preparation: Add 23 g of Nutrient Agar to 1 L of reagent-grade distilled water, and mix 

well. Heat to boiling to dissolve the agar completely. Dispense in screwcap tubes, and 

autoclave at 121°C (15 lb pressure) for 15 min. Remove the tubes and slant. Final pH 

should be 6.8 ± 0.2. 

7.8 Tryptic Soy Broth (Difco 0370); Trypticase Soy Broth (BD 99071) 

7.8.1 Composition: 

Tryptone or Trypticase 17.0 g 

Soytone or Phytone 3.0 g 

Sodium Chloride 5.0 g 

Dextrose 2.5 g 

Dipotassium Phosphate 2.5 g 

Reagent-Grade Distilled Water 1.0 L 

7.8.2 Preparation: Add 30 g of dehydrated Tryptic/Trypticase Soy Broth to 1 L of reagentgrade distilled water. Warm the broth, and mix gently to dissolve the medium 

completely. Dispense in screw-cap tubes, and autoclave at 121°C (15 lb pressure) for 15 

min. Final pH should be 7.3 ± 0.2. 

7.9 Simmons Citrate Agar (Difco 0091, BD 4311620) 

7.9.1 Composition: 

Magnesium Sulfate 0.2 g 

Monoammonium Phosphate 1.0 g 

Dipotassium Phosphate 1.0 g 

Sodium Citrate 2.0 g 

Sodium Chloride 5.0 g 

Brom Thymol Blue 0.08 g 

Agar 15.0 g 

Reagent-Grade Distilled Water 1.0 L 

7.9.2 Preparation: Add 24.2 g Simmons Citrate Agar to 1 L of reagent-grade distilled water. 

Heat to boiling to dissolve completely. Dispense into screwcap tubes, and autoclave at 

121°C (15 lb pressure) for 15 min. Cool the tubes and slant. Final pH should be 6.8 ± 

0.2. 

7.10 Tryptone 1% (Difco 0123); Tryptophane Broth (BD 4321717 and 4321718) 

7.10.1 Composition: 

Tryptone or Trypticase Peptone 10.0 g 

Reagent-Grade Distilled Water 1.0 L 

7.10.2 Preparation: Add 10 g tryptone or trypticase peptone to 1 L or reagent-grade distilled 

water, and heat, mixing until dissolved. Dispense in 5-mL volumes into tubes, and 

autoclave 121°C (15 lb pressure) for 15 min. Final pH should be 7.2 ± 0.2. 

7.11 EC Broth (Difco 0314, BD 4311187) 

7.11.1 Composition: 

Tryptose or Trypticase Peptone 20.0 g 

Lactose 5.0 g 

Bile Salts no. 3 or Bile Salts Mixture 1.5 g 

Dipotassium Phosphate 4.0 g 

Monopotassium Phosphate 1.5 g 

5 September 2002 
Method 1603 

Sodium Chloride 5.0 g 

Reagent-Grade Distilled Water 1.0 L 

7.11.2 Preparation: Add 37 g dehydrated EC medium to 1 L of reagent-grade distilled water, and 

warm to dissolve completely. Dispense into fermentation tubes (20 x 150 mm tubes 

containing inverted 10 x 75 mm vials). Autoclave at 121°C (15 lb pressure) for 15 min. 

Final pH should be 6.9 ± 0.2. 

7.12 Oxidase Reagent 

7.12.1 Composition: 

N, N, N’, N’-tetramethyl-D-phenylenediamine dihydrochloride, 1% aqueous 

solution (1 g per 100 mL sterile reagent-grade distilled water). 

7.13 Kovacs Indole Reagent 

7.13.1 Composition: 

D-dimethylaminobenzaldehyde 10.0 g 

Amyl or Isoamyl Alcohol 150.0 mL 

Concentrated (12 M) Hydrochloric Acid 50.0 mL 

7.13.2 Preparation: Dissolve D-dimethylaminobenzaldehyde in alcohol, slowly add hydrochloric 

acid, and mix. 

8.0 Sample Collection, Preservation, and Storage 

8.1 Sampling procedures are described in detail in the USEPA microbiology methods manual, 

Section II, A (Reference 18.2). Adherence to sample preservation procedures and holding time 

limits is critical to the production of valid data. Samples not collected according to these rules 

should not be analyzed. 

8.1.1 Storage Temperature and Handling Conditions 

Ice or refrigerate water samples at a temperature of 1-4°C during transit to the laboratory. 

Use insulated containers to assure proper maintenance of storage temperature. Take care 

that sample bottles are not totally immersed in water during transit or storage. 

8.1.2 Holding Time Limitations 

Examine samples as soon as possible after collection. Do not hold samples longer than 

6 h between collection and initiation of analyses. 

9.0 Quality Control 

9.1 See recommendations on quality control for microbiological analyses in the USEPA 

microbiology methods manual, Part IV, C (Reference 18.2). 

10.0 Calibration and Standardization 

10.1 Check temperatures in incubators daily to ensure operation within stated limits. 

10.2 Check thermometers at least annually against a NIST certified thermometer or one that meets the 

requirements of NIST Monograph SP 250-23. Check mercury columns for breaks. 

11.0 Procedure 

September 2002 6 
Method 1603 

11.1 Prepare the modified mTEC Agar as directed in section 7.6. 

11.2 Mark the petri dish and report form with the sample identification and volume. 

11.3 Place a sterile membrane filter on the filter base, grid side up, and attach the funnel to the base so 

that the membrane filter is held between the funnel and the base. 

11.4 Shake the sample bottle vigorously at least 25 times to distribute the bacteria uniformly, and 

measure the desired volume of sample or dilution into the funnel. 

11.5 Select sample volumes based on previous knowledge of the pollution level, to produce 20-80 E. 

coli colonies on the membranes. Sample volumes of 1-100 mL are normally tested at half-log 

intervals (e.g., 100, 30, 10, 3 mL). 

11.6 Smaller sample sizes or sample dilutions can be used to minimize the interference of turbidity or 

for high bacterial densities. Multiple volumes of the same sample or sample dilutions may be 

filtered, and the results may be combined. 

11.7 Filter the sample, and rinse the sides of the funnel at least twice with 20-30 mL of sterile buffered 

rinse water. Turn off the vacuum, and remove the funnel from the filter base. 

11.8 Use sterile forceps to aseptically remove the membrane filter from the filter base, and roll it onto 

the modified mTEC Agar to avoid the formation of bubbles between the membrane and the agar 

surface. Reseat the membrane if bubbles occur. Run the forceps around the edge of the filter to 

be sure that the filter is properly seated on the agar. Close the dish, invert, and incubate 35 ± 

0.5°C for 2 h. 

11.9 After a 2 h incubation at 35 ± 0.5°C, transfer the plate to a Whirl-Pak® bag, seal the bag, place 

the bag with the plate inverted in a test-tube rack, and put the rack in a 44.5 ± 0.2°C waterbath for 

22-24 h. 

11.10 After 22-24 h, remove the plate from the waterbath, count and record the number of red or 

magenta colonies with the aid of an illuminated lens with a 2-5x magnification or a stereoscopic 

microscope (See Photo 1). 

12.0 Data Analysis and Calculations 

Use the following general rules to calculate the E. coli count per 100 mL of sample: 

12.1 Select the membrane filter with an acceptable number of magenta or red colonies (20-80), and 

calculate the number of E. coli per 100 mL according to the following general formula: 

Number of E. coli colonies 

E. coli/100 mL = X 100 

Volume of sample filtered (mL) 

12.2 See the USEPA microbiology methods manual, Part II, Section C, 3.5, for general counting rules 

(Reference 18.2). 

12.3 Reporting Results 

12.3.1 There should be at least three volumes filtered per sample. Report the results as E. coli 

per 100 mL of sample. 

13.0 Method Performance 

13.1 The false-positive and false-negative rates, reported for various environmental water samples, 

were <1% and 4%, respectively. 

7 September 2002 
Method 1603 

14.0 Reporting Results 

14.1 There should be at least three volumes filtered per sample. Report the results as E. coli per 100 

mL of sample. 

15.0 Verification Procedure 

15.1 Red or magenta colonies can be verified as E. coli. Verification of colonies may be required in 

evidence gathering and is also recommended as a means of quality control for the initial use of 

the test and for changes in sample sites, lots of commercial media, or major ingredients in media 

compounded in the laboratory. The verification procedure follows. 

Photo 1. Escherichia coli colonies on modified mTEC agar. E. coli colonies are red to magenta. 

15.2 Using a sterile inoculation loop, transfer growth from the centers of at least 10 well-isolated 

colonies to Nutrient Agar plates or slants and to Trypticase Soy Broth. Incubate the agar and 

broth cultures for 24 h at 35 ± 0.5°C. 

15.3 After incubation, remove a loopful of growth from the Nutrient Agar slant with a platinum loop, 

and deposit it on the surface of a piece of filter paper that has been saturated with freshly prepared 

Cytochrome Oxidase Reagent. If the spot where the bacteria were deposited turns deep purple 

within 15 seconds, the test is positive. 

15.4 Transfer growth from the Trypticase Soy Broth tube to Simmons Citrate Agar, Tryptone Broth, 

and an EC Broth fermentation tube. 

15.4.1 Incubate the Simmons Citrate Agar and Tryptone Broth for 48 h at 35 ± 0.5°C. 

15.4.2 Incubate the EC Broth at 44.5 ± 0.2°C in a waterbath for 24 h. The water level must be 

above the level of the EC Broth in the tube. 

15.4.3 Add 0.5 mL of Kovacs Indole Reagent to the 48 h Tryptone Broth culture, and shake the 

tube gently. A positive test for indole is indicated by a deep red color which develops in 

the alcohol layer on top of the broth. 

15.4.4 E. coli is EC gas-positive, indole-positive, and oxidase-negative, and does not utilize 

citrate (i.e., the medium remains green). 

September 2002 8 
Method 1603 

15.5 Alternately, commercially available multi-test identification systems may be used to verify 

colonies. Inoculate the colonies into an identification system for Enterobacteriaceae that 

includes lactose fermentation, F-nitrophenyl-$-D-galactopyranoside (ONPG), and cytochrome 

oxidase test reactions. 

16.0 Pollution Prevention 

16.1 The solutions and reagents used in this method pose little threat to the environment when 

recycled and managed properly. 

16.2 Solutions and reagents should be prepared in volumes consistent with laboratory use to minimize 

the volume of expired materials to be disposed. 

17.0 Waste Management 

17.1 It is the laboratory's responsibility to comply with all federal, state, and local regulations 

governing waste management, particularly the biohazard and hazardous waste identification rules 

and land disposal restrictions, and to protect the air, water, and land by minimizing and 

controlling all releases from fume hoods and bench operations. Compliance with all sewage 

discharge permits and regulations is also required. 

17.2 Samples, reference materials, and equipment known or suspected to have viable E. coli attached 

or contained must be sterilized prior to disposal. 

17.3 Samples preserved with HCl to pH <2 are hazardous and must be neutralized before being 

disposed, or must be handled as hazardous waste. 

17.4 For further information on waste management, consult “The Waste Management Manual for 

Laboratory Personnel” and “Less Is Better: Laboratory Chemical Management for Waste 

Reduction,” both available from the American Chemical Society's Department of Government 

Relations and Science Policy, 1155 16th Street NW, Washington, DC 20036. 

18.0 References 

18.1 Annual Book of ASTM Standards, Vol. 11.01, American Society for Testing and Materials, 

Philadelphia, PA 19103. 

18.2 Bordner R., J.A. Winter, P.V. Scarpino (eds.). 1978. Microbiological methods for Monitoring 

the Environment: Water and Wastes, EPA-600/8-78-017. Office of Research and Development, 

USEPA. 

18.3 Cabelli, V.J., A.P. Dufour, M.A. Levin, L.J. McCabe, and P.W. Haberman. 1979. Relationship of 

Microbial Indicators to Health Effects at Marine Bathing Beaches. Am. J. Public Health. 69: 

690-696. 

18.4 Improved Enumeration Methods for the Recreational Water Quality Indicators: Enterococci and 

Escherichia coli. 2000. EPA/821/R-97/004. Office of Science and Technology, Washington D.C. 

18.5 Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, 

Washington, DC. For suggestions of the testing of reagents not listed by the American Chemical 

Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, UK and the 

United States Pharmacopeia. 

18.6 Test methods for Escherichia coli and Enterococci in Water by the Membrane Filter Procedure. 

1985. EPA-600/4-85/076. Environmental Monitoring and Support Laboratory, Cincinnati, 

USEPA. 

9 September 2002